1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a turbine stator vane with endwall cooling.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream.
In the prior art, vane endwall cooling is produced using backside impingement cooling in a middle region of the vane endwall with the spent impingement cooling air being discharged around the side edges of the endwall to provide for both cooling and sealing of the endwall. Discharge cooling air holes are drilled through the endwall and into an impingement cavity located at the middle of the vane endwall from both mate faces as well as from the endwall leading and trailing edges. The overall cooling effectiveness level for this design is very low, especially around the edges of the endwall. FIG. 1 shows a prior art stator vane with two airfoils extending between inner and outer diameter endwalls.
FIG. 2 shows a cross section top view of the endwall of FIG. 1 with the cooling circuit. Two airfoils 11 extend between endwalls and form an impingement cavity 12. Impingement cooling air holes 13 open into the impingement cavity to discharge impingement cooling air against the backside surface of the endwall. Leading edge cooling holes 14 discharge cooling air along the leading edge side of the endwall. Trailing edge cooling holes 15 discharge cooling air along the trailing edge side of the endwall. Mate face cooling holes 16 discharge cooling air from the two mate faces of the endwall. The cooling air holes 14-16 that provide cooling for the endwall are all connected to the impingement cavity 12 and discharge from all four edges of the endwall. The cooling air holes 14-16 are all straight cooling air holes that provide convection cooling only.